The Radio Frames in the Long Term Evolution (LTE) system include frame structures of the Frequency Division Duplex (FDD) mode and the Time Division Duplex (TDD) mode.
The frame structure of the FDD mode is shown in FIG. 1, a 10 ms radio frame is composed of 20 0.5 ms slots that are numbered as 0˜19, and the slots 2i and 2i+1 compose of the 1 ms subframe i.
The frame structure of the TDD mode is shown in FIG. 2, a 10 ms radio frame is composed of 2 5 ms half frames, one half frame comprises 5 1 ms subframes, and the subframe i is defined as two 0.5 ms slots 2i and 2i+1.
In the aforementioned two frame structures, for the standard Normal Cyclic Prefix (Normal CP), one slot contains 7 66.7 us symbols, wherein the length of the CP of the first symbol is 5.21 us, and the length of the rest 6 symbols is 4.69 us; for the Extended Cyclic Prefix (Extended CP), one slot contains 6 symbols, and the length of the CP of all the symbols is 16.67 us.
The LTE system also defines the following three kinds of downlink physical control channels: the Physical Control Format Indicator Channel (PCFICH); the Physical Hybrid Automatic Retransmission Request Indicator Channel (PHICH); the Physical Downlink Control Channel (PDCCH), wherein:
(1) the information born on the PCFICH is used to indicate the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols for transmitting the PDCCH in one subframe, it is transmitted in the first OFDM symbol of the subframe, and all the frequency locations are determined according to the system downlink bandwidth and cell Identity (ID).
(2) The PHICH is used to bear the Acknowledgement/Negative Acknowledgement (ACK/NACK) feedback information of the uplink transmission data. The number of PHICHs and the time-frequency locations are determined by the system messages and cell ID in the Physical Broadcast Channel (PBCH) of the downlink carrier where the PHICH is located.
(3) The PDCCH is used to bear the Downlink Control Information (DCI), including: uplink and downlink scheduling information, as well as uplink power control information. The PDCCH DCI format (format) is divided into: DCI format 0, DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, DCI format 1D, DCI format 2, DCI format 2A, DCI format 3, and DCI format 3A, and so on; wherein:
the DCI format 0 is used to indicate the scheduling of the Physical Uplink Shared Channel (PUSCH);
the DCI format 1, the DCI format 1A, the DCI format 1B, the DCI format 1C, and the DCI format 1D are used to indicate different modes of one PDSCH codeword scheduling;
the DCI format 2 and the DCI format 2A are used to indicate different modes of the space division multiplexing;
the DCI format 3 and the DCI format 3A are used to indicate different modes of the power control instructions of the Physical Uplink Control Channel (PUCCH) and the PUSCH.
The PDCCH search space is divided into a common search space and a UE-specific search space, and the common search space is the space that all the UEs need to search, and the UE-specific search space is the specific search space for one UE. Both the common search space and the UE-specific search space correspond to respective DCI Formats. The UE respectively detects the corresponding downlink control information in the common search space and the UE-specific search space in accordance with the corresponding DCI Formats.
The PDCCH corresponds to four levels that are also known as four PDCCH Formats, respectively corresponding to 1 Control Channel Element (CCE), 2 CCEs, 4 CCEs and 8 CCEs.
The protocol of the LTE whose version corresponds to the Release (R) 8 defines six kinds of bandwidths as follows: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. The ITE-Advanced (Further Advancements for E-UTRA) is the evolved version of the LTE Release-8. The ITE-Advanced should also meet or exceed the requirements of IMT-Advanced proposed by the International Telecommunication Union (ITU-R) besides meeting or exceeding the 3rd Generation Partnership Project (3GPP) TR 25.913: “requirements for Evolved Universal Telecommunication Radio Access (Evolved UTRA) and Evolved Universal Telecommunication Radio Access Network (Evolved UTRAN)”.
The requirements of the backward compatible with the LTE Release-8 refer that: the LTE Release-8 terminal can work in the LTE-Advanced network; the LTE-Advanced terminal can work in the LTE Release-8 network.
In addition, the LTE-Advanced should work in different size spectrum configurations, including working in spectrum configuration (such as the 100 MHz continuous spectrum resources) wider than that of the LTE Release-8 so as to achieve higher performances and target peak rates. Take into account the compatibility with the LTE Release-8, for a bandwidth larger than 20 MHz, the carrier aggregation way is used, namely:                two or more component carriers are aggregated to support downlink transmission bandwidth larger than 20 MHz; and        the terminal can receive one or more component carriers at the same time according to its capability.        
The LTE-A terminal with a receiving capability more than 20 MHz bandwidth is capable of simultaneously receiving the transmission on a plurality of carrier components. The LTE Rel-8 terminal can only receive the transmission on one component carrier, and the structure of the component carrier follows the Rel-8 specification.
At present, the downlink control signaling transmission, that is the form of the Physical Downlink Control Channel (PDCCH), in the LTE-Advanced standard has the following conclusions:                Define a User Equipment (UE) specified Downlink Component Carrier Set used for transmitting the Physical Downlink Shared Channel (PDSCH) scheduled to the target UE, and the carrier set is notified with a special signal.        Backward compatible carrier can allow the access of the UEs of all the existing LTE versions, and can operate in the form of single-carrier (stand-alone) or act as a part of spectrum aggregation. For the FDD, the backward compatible carriers always appear in pairs, that is, downlink (DL) and uplink (UL).        Non-backward compatible carrier can be defined as allowing the access of the UE of the LTE version of such a kind of carriers if defined, but cannot allow the access of the UE of the LTE R8 version. If the non-compatibility is derived from the frequency multiplexing distance, the non-backward compatible carrier operates in the form of single-carrier (stand-alone), or acts as a part of the spectrum aggregation.        Extended carrier: cannot operate in the form of single carrier if defined, but must be a composition part of a carrier group, and at least one carrier in the carrier group is able to operate in the form of single-carrier (stand-alone).        The PDCCHs on one component carrier indicates the PDSCH resources of the same component carrier and the PUSCH resources of the only one connected uplink component carrier.        There is no carrier indicator field in the DCI format                    i.e., the PDCCH structure (the same encoding and the same CCE based resource mapping) and DCI formats in the Rel-8 version.                        The PDCCHs on one component carrier use the carrier indicator field to indicate the PDSCH or PUSCH resources of one component carrier in multiple component carriers.        The extended 1 to 3 bits carrier indicator field (CI) in the DCI formats in the Rel-8                    reuses the Rel-8 PDCCH structure (the same encoding and the same CCE based resource mapping).                        It needs to study the solution of the detection error of the PCFICH of the component carrier bearing the PDSCH        The existence of the carrier indicator (CI) field is configured semi-statically.        
When the extended carrier scheduling is allowed, since each carrier might correspond to different DCI Format types, the UE needs to perform large amount of blind detection on the downlink component carrier to be detected to determine the downlink control information transmission condition configured by the base station, which increases the implementation complexity and results in the system performance degradation. In addition, due to the introduction of cross-carrier scheduling, it means that the downlink control information configured by the base station can be centralized on one or more downlink component carriers in the UE specific downlink component carrier set to be transmitted.
Due to the introduction of cross-carrier scheduling and carrier aggregation, there are problems that the number of blind detections will increase and how to transmit and detect the multi-carrier downlink control information, and so on.